\begin{tikzpicture}
    \tkzDefPoints{0/0/B, 4/0/C,  1/2/A,  3.5/2/D}

    \tkzDrawPolygon(A,B,C,D)
    \tkzLabelPoints[below](B,C)
    \tkzLabelPoints[above](A,D)
\end{tikzpicture}

